I don't know what the connectors are in the first picture. I think the solo wire is part of the original stereo's antitheft feature. You don't need it in for the replacement stereo.

The wires in the second picture include the hot wire (for clock and station preset memory), switched power and ground. Maybe the antenna wire is in there as well. You'll have to get a diagram or use a tester to figure out which is which. Brown is usually ground in these cars.

The wires in the third picture go to the thumbwheel fader behind the shifter.

You have a choice of using the front OR rear speaker outputs of the replacement stereo and the existing fader, or using the front AND rear speaker outputs of the replacement stereo and bypassing the existing fader. If you go with the second approach, you have the choice of tapping into the speaker harness downstream of the existing fader by hooking up the each channel (left and right) in a common ground arrangement (does the replacement stereo support this?), or using the existing speaker connectors in the stereo cavity to drive the rear speakers (keep the existing fader centered or full rear), and run new wires to the dash speakers.

Good luck.

Sixto
95 S420
87 300SDL